Numerous types of conveyors can be used in manufacturing facilities. In some embodiments, the conveyor can be a linear synchronous motor (LSM) based system that facilitates propulsion of vehicles along the track using electromagnetic force (EMF). MagneMotion, Inc. of Devens, Mass., U.S.A., and other companies hold a number of patents directed to such systems. Patent publications directed to such systems include the following: U.S. Pat. No. 6,011,508, Perreault, et al.; U.S. Pat. No. 6,101,952, Thornton, et al.; U.S. Pat. No. 6,499,701, Cho; U.S. Pat. No. 6,578,495, Yitts, et al.; U.S. Pat. No. 6,781,524, Clark, et al.; U.S. Pat. No. 6,917,136, Thornton, et al.; U.S. Pat. No. 6,983,701, Thornton, et al.; U.S. Pat. No. 7,011,728 B2, Dewig, et al.; U.S. Pat. No. 7,264,426 B2, Buttrick, Jr.; U.S. Pat. No. 7,448,327, Thornton, et al.; U.S. Pat. No. 7,458,454, Mendenhall; U.S. Pat. No. 8,591,779 B2, Senn, et al.; U.S. Pat. No. 9,032,880, Senn, et al.; U.S. Pat. No. 9,233,800 B2, Senn, et al.; U.S. Pat. No. 9,283,709 B2, Lindner, et al.; US Patent Application Publication US 2016/114988 A1; and, EP Patent 1 645 340 B1.
When manufacturing products such as liquid, powder, and other such products that are packaged in bottles or other containers, it is desirable to weigh each container after it has been filled to ensure that the container contains the proper amount of the product. Manufacturing systems using traditional belt or chain conveyors typically include a “checkweigher” along the conveyor to measure the weight of the filled containers. Some checkweighers require that the article be stationary when it is weighed. Other checkweighers are capable of weighing the filled containers when the containers are in motion while being conveyed by the conveyor. Still other systems require that the articles be removed from the conveyor in order to weigh each article.
Linear synchronous motor conveyor systems present particular challenges when it is desired to weigh an article being conveyed (that is, while the article is in motion) on the LSM conveyor. It was previously thought that placing a linear motor conveyor on top of a weigh cell would not work for several reasons. First, linear synchronous motor conveyors typically employ vehicles to convey the articles around the track. The weight of these vehicles must be subtracted from the weight measurement. Second, linear synchronous motors are relatively heavy in comparison to the article being weighed and present a large “dead load” that would need to be weighed along with the article. Third, linear synchronous motors have power and communication cables attached thereto that would have to be part of the weight measurement. Fourth, linear synchronous motor conveyors are typically comprised of sections of track. There can be small gaps between the sections of track that the object to be weighed will have to traverse as it transitions onto and off of the weigh cell. When the object travels over these gaps, this can cause vibrations in the weigh cell and the object being weighed, both of which can cause errors in the measured weight. Such errors can be further compounded when measuring the weight of liquids in moving containers due to the tendency of liquids to “slosh” or move inside the containers. Fifth, checkweighers are typically used in production systems to weigh many of the same general size and weight of articles for long periods of time during that production run. It is desirable to use a checkweigher on a production line that is capable of producing a wide variety of different size and weight of articles in which there may be a large swing in total weight from one measurement to the next.
Thus, there is a need for a weigh-in-motion scale system that can be used on a linear synchronous motor conveyor. In particular, there is a need for a weigh-in-motion scale system that can be used on a high speed linear synchronous motor conveyor that can weigh articles with a relatively wide variety of weights with high accuracy.